Originally posted by Phobos It's probably best to stick with the idea that the universe is boundless and has no external reality, therefore, it has no shape.

I think that's rather misleading. I suppose it depends on what you mean by "shape", but the universe certainly does have a geometry, regardless of whether it is bounded, embedded in some external space, or whatever.

Originally posted by Ambitwistor We have no idea. We don't even know if it's finite or infinite.

From what I hear,a current study checking the validty (against other cosmological evidence) of non-trivial topologies which give the observed degree of curvature (i.e. almost flat) is almost finished and has managed to eliminate all the non-trivial topologies tested so far, which suggests (though this obviously can't be a conclusion) that the universe is flat and infinite.

I understand the ideas of 'flat', 'unbounded', 'open' etc, but is there any meaningful way in which we can imagine what this means in a non-mathematical way?
In other words, back to my original question - is it possible to visualise the shape, or possible shapes, of the universe? I personally think not, but wondered if anyone had ever tried to explain the possible shape in a manner which we can visualise?

On another, but related point - can you point me towards links (or explain) the latest thoughts on how the expansion rate of the Universe is somehow increasing.

In other words, back to my original question - is it possible to visualise the shape, or possible shapes, of the universe?

Sort of, but it's hard. Read The Shape of Space by Weeks.

On another, but related point - can you point me towards links (or explain) the latest thoughts on how the expansion rate of the Universe is somehow increasing.

Right now, there is very far from a consensus on the topic. Some people propose a cosmological constant, some propose quintessence (a field which produces a dynamical, effective cosmological constant), etc. The June 20, 2003 issue of Science has some articles on dark energy.

would it not be best to say, to date we know nothing about
the shape size of the universe ,if it is bounded
unbounded, or even what it is composed of, theories abound
but facts are nonexistant, it all comes down to probability,
even that is a human concept

Actually, for the past 30 years we've been hearing radio waves from the big bang origin. Its a neer silent hush, but we've also succeeded in "mnapping" these waves by their frequencies, this should indicate the "end of the universe" and we have found that the end of the universe is blotchy....wierd, but perhaps this is just the end of our physical universe, and the start of another.

What I see so far is that the universe is even wierder than science fiction. I think that the fact that our most basic laws of physics are being wuestion is a hell of a lot more wierd than super laser beams..

Originally posted by jcsd From what I hear,a current study checking the validty (against other cosmological evidence) of non-trivial topologies which give the observed degree of curvature (i.e. almost flat) is almost finished and has managed to eliminate all the non-trivial topologies tested so far, which suggests (though this obviously can't be a conclusion) that the universe is flat and infinite.

Phobos, the 'soccer ball' shape has as far as I know been elimanted.

Where did this "soccer ball" shape come from anyway? I read about it in the news, but I couldn't find any supporting facts (of course, I didn't look that hard either).

The first thing I thought of was Plato, because of his dodecahedral Platonic solid being representative of the universe as a whole. It would seem historically significant if the universe were found to have such a "shape", because there are 12 pentagons (Pythagoreans, golden ratio, etc.) each surrounded by hexagons in a soccer ball.

I don't know what inspired them to look at this shape, but basically some showed mathemtically that this shape could produce a curvature within the error margin ofd the observed curvature of the universe.

People looked at correlations between the temperature of the cosmic background radiation in different directions in the sky. There may be a lack of correlations on large scales, meaning that some large wavelengths might be excluded from the spectrum, implying that the universe isn't big enough to support waves that big. From the pattern of correlations, the geometry of space can be reconstructed, and they found that a dodecahedral geometry fit the pattern best. However, a different kind of correlation search failed to support that hypothesis:

Originally posted by Ambitwistor And no, your description isn't right even for a spherical universe: the Big Bang was not an explosion that blasted a spherical wavefront outwards from some central point.

I know your are right, but this model is the one all my students think of when I'm teaching them about Big Bang theory. I'd like to lead them to think about it in another way, but sadly I just can't think of anyway of visualising the shape. This was why I asked my original question.

I didn't think that there would be a simple way of visualising the shape of the Universe, but how about another challenge then..
(its my challenge actually but I've obviously failed )

You have a class of very bright 17/18 year old Physics students who want to try to understand Big Bang theory and the shape of the Universe.

- How do you get them to visualise it (or to STOP trying to..)

- If it is expanding, is there an edge? If not why not?

I can cope with all the other questions, but these two just seem to get me every time...

You have a class of very bright 17/18 year old Physics students who want to try to understand Big Bang theory and the shape of the Universe.

- How do you get them to visualise it (or to STOP trying to..)

- If it is expanding, is there an edge? If not why not?

Well, if you want to use the 2D balloon analogy, you can try that... but you have to emphasize that in this analogy, space is the surface of the balloon; there is no interior or exterior of the balloon, and no higher-dimensional space that the balloon is expanding "into" --- we only visualize the 2D balloon as sitting inside of a 3D space for the purposes of visualization.

In this model, space has no edge for the same reason we don't fall off the edge of the Earth: the Earth's surface has no boundary.

If they can't get past the idea that the universe is expanding "into" something, because the balloon is getting bigger, have them imagine the balloon staying the same size and everything in it as shrinking. There is no physical distinction between the two cases.

But because of these embedding issues, it may be better to use a flat universe analogy, where the universe is regarded as a 2D plane, instead of a sphere. It's easier to think of that without imagining it sitting inside some other space. Picture a bunch of dots scattered within the plane, and then zooming in or out of the plane: at any time, the plane is completely filled with a random collection of dots (though their average spacing may change), but there is no center or edge of the plane.

The “soccer ball” shape is really a Dodecahedron. ANY finite unbounded 2-dimensional surface, such as a Sphere, Torus or Klein Bottle, can be described topologically in terms of a Polygon with the edges identified.